1. Field of the Invention
The present invention generally relates to shot-shells and, more particularly, is concerned with an improved composite shot wad structure for a shotshell having a unique laminated shot pocket portion adapted for used with hard shot, such as steel or tungsten shot. 2. Description of the Prior Art
"Lightweight" as used herein means substantially lighter than lead (i.e. lighter than 11 gm/cc density).
"Deformation resistant" as used herein means having an ultimate tensile strength greater than 4000 psi.
It is conventional practice to provide plastic wad structures for use in shotshells to house the shot charge, obturate combustion gases, and cushion the shot charge when the loaded wad is fired from a shotgun. One wad structure representative of this practice is illustrated and described in U.S. Pat. No. 3,285,174 to V. C. Moehlman et al., which patent issued Nov. 15, 1966 and is assigned to the assignee of the present invention.
Typically, the was structure has a unitary one-piece construction and is composed of a shot pocket portion, a filler or cushioning portion and an obturating portion. The shot pocket portion is shaped like a cup and includes a cylindrical split side wall open at the top and closed at the bottom. The obturating portion has a shallow cup-like shape and includes a base with a peripheral flared skirt. The cushioning portion generally includes a series of flexible members which extend between and interconnect the other two portions of the wad structure.
When a shotshell containing the above-described wad structure is loaded in a shotgun and fired, a propellant disposed in the shell tube rearwardly of the obturating portion is consumed and produces high pressure combustion gases. The pressurized gases act upon the obturating portion, causing its skirt to expand outwardly into sealing relationship with the inner surface of the shell tube and wall of the gun barrel bore. Such sealing increases the compressive forces being generated by the pressurized combustion gases. Since the column of shot pellets contained in the shot pocket portion of the wad structure initially resists forward movement, the compressive forces first compress the cushioning portion of the wad structure. Then, as the wad structure and shot column are propelled out of the shell tube and start to accelerate through the gun barrel, the shot column pushes radially outward toward the wall of the barrel bore and against the sidewall of the shot pocket portion.
There have, in the past, been a number of attempts made to vary or modify such a wad design like that of the Moehlman et al. U.S. Pat. No. 3,285,174 in order to decrease the dispersion of the shot by adding additional components, such as a closed pouch to hold the shot for longer than normal (e.g. Lathrop et al.'s U.S. Pat. No. 3,516,360 issued June 23, 1970) or a heavy deformable lead liner to entrain the shot (e.g. British Pat. No. 9756). However, these have limited utility, the shotgun hunter normally desires a certain amount of dispersion, as otherwise he would use a rifle with a single bullet, so such dispersion decreasers are often counter-productive in that they decrease the velocity of the shot by adding parasitic weight. Maximum velocity is usually desired to minimize the required "lead angles" when shooting moving targets (e.g. waterfowl or upland game).
Historically, shot pellets have been composed of lead which is much softer than the metal traditionally composing the gun barrel. Therefore, an important objective of the shot pocket portion of the wad structure heretofore has been to prevent contact of the softer shot pellets with the harder barrel in order to prevent leading of the barrel and distortion of the shot pellets. This objective of lead shot protection has been satisfactorily attained by the shot pocket portion design disclosed in the aforesaid patent.
However, due to the toxicity of lead and health concerns about possible retention of lead shot in game intended for human consumption, laws have recently been enacted in may states which substantially limit or even ban the use of traditional lead shot pellets in hunting game and mandate the use of hard materials having little or no known toxicity, such as steel. In military shotguns, the recently developed Olin shotshells use extremely hard shot (for armor penetration) such as tungsten. While formerly in the case of lead shot pellets, the objective of the shot pocket portion was to protect the softer shot pellets from deformation by the harder gun barrel, now in the case of steel or tungsten shot pellets, the new objective is to protect the softer gun barrel from the harder shot pellets.
The shot pocket portions of wad structures designed for use with lead shot pellets have proven unable to meet this new objective. The plastic materials used heretofore fail to withstand the compressive forces of the hard shot. The shot readily penetrates through the sidewall of the pocket portion and contact the barrel wall, causing marring or scoring thereof. Merely making the plastic material heavier or thicker or substituting a stronger plastic material has not been found to provide workable and economical solution to the problem of preventing barrel scoring. Plastic materials that are strong enough to withstand the force of the steel shot are usually expensive and, in some cases, too stiff to allow proper obturation of the propellant gases in cold weather.
This new objective appears to require the use of a plastic material that has two entirely different sets of properties--high tensile strength for barrel protection and high ductility for proper obturation. Seemingly, one way around this requirement would be to design a two-piece wad, the top of which is hard, tough plastic material and the bottom of which is a soft plastic material which obturates easily. A two-piece plastic wad is, however, expensive in that it requires two separate molding operations and an assembly operation. The cost of these requirement would be prohibitive in terms of producing a competitively priced shotshell.
Consequently, a need exists to come up with a solution which will provide the two different properties mentioned above, but will be workable and economical in the sense that it takes advantage of conventional mass-production fabrication techniques.